A big barrier to growth is an immigration policy that deprives the UK of skilled workers in certain disciplines. Lord Heseltine, while at pains to avoid criticising the Government, clearly sympathises with the difficulties that businesses face in recruiting these workers.

O'Donnell's criticism piles on the pressure the government is facing to justify its immigration policy in economic, as well as just populist, terms. As he mentioned, Heseltine's review, No stone unturned(pdf), also tactfully steers a course rather different to that currently being pursued by the Home Office.

Heseltine writes:

It goes almost without saying that the ideal solution is a well-managed immigration system that is open and welcoming to those who can address our skills gaps and add value to the economy, yet is unattractive to those who do not have and would not get permission to be here. This is easier said than done at a time of tough manpower constraints in the public sector.

While it "almost goes without saying", that is not actually the government's own strategy. The Conservatives are locked into a damaging attempt to bring net migration in under an arbitrary cap; and worse, they have no power to affect the biggest single contributor to that number, which is intra-EU migration.

As a result, the party is forced to attack the small sliver of migration they can have an effect on. But unskilled, non-EU migration had already been extremely constrained by the previous government, so to limit immigration any further, skilled migration came under fire. Even with new strict measures on visas, the government is losing the fight miserably. Its target is net migration of 100,000 people; the latest figures show that number is 216,000.

Politically the government is failing. It has set itself a challenge which it will not – cannot – meet. That alone would be a reason for abandoning the aim now, nobly accepting defeat, even if that figure weren't one which no sane government ought to try to achieve.

The country has, in effect, installed a “keep out” sign over the white cliffs of Dover. Even as Mr Cameron defends the City of London as a global financial centre, and takes planeloads of business folk on foreign trips, his government ratchets up measures that would turn an entrepôt into a fortress. In the past two years the Tories have made it much harder for students and foreign workers and family members to enter and settle in the country. Britain is not only losing the war for global talent, it is scarcely competing. More people now leave to take up job offers in other countries than come the other way.

In fact, even the nascent pro-immigration voices on the right don't take the argument far enough. While many of them are content to make the argument that immigration represents a favourable trade-off between unemployment and growth, few take the extra step of point out that immigration can help with both employment and growth. This argument involves tackling head-on the pervasive "lump of labour" fallacy – the idea that there are a fixed number of jobs, and if a foreigner gets one, then a Briton can't.

Imagine the worst case scenario in Cringely’s mind occurs, and a foreign worker takes a job at a 30% discount, and a native worker who could have had the job has to settle for a lower paying job. To understand the impact on U.S. workers you have to look beyond this worker who has had his job “stolen”, and must look at what economists call the general equilibrium effect. Here are other things that happen: the H1-B worker buys or rents a home, and a landlord of home seller benefits, overall, new houses will be built, meaning construction workers benefit. The H1-B worker shops at a grocery store, which employs workers, and sells goods made by farmers who also employ workers. See how this goes?

The economic case for limiting migration is thoroughly lost. At best, the government is now facing the risk that this argument filters into the popular perception; at worst, it is in the position of encouraging a popular attitude which is simply incorrect.